Oscillation generation



June 17, 1941 w. VAN B. ROBERTS 2,245,718

OSCILLATION GEIIIERATION Filed Jan. 7, 1939 INVENTOR. W4L TER V N 5.ROBERTS A TTORNEY.

Patented June 17, 1941 STATES AT Waltcr'van Roberts, Princeton; N.' J l,.assignor 1 to RadioOorp'oration of America, 'a corporation of DelawareThe present invention relates to an oscillator circuit of the typeemploying degeneration to improve its stability; I 4

The primary object of the invention isto simplif'y the stabilizationof,v oscillation generator systems. In one embodiment of the inventionthe frequency of oscillation is stabilized, while in another embodimentboth frequency and amplitude of oscillation are stabilized.

A better understanding of the invention may be had by referring to thefollowing description, which is accompanied by a drawing wherein Figs. 1and 2 show, by way of example only, two oscillation generation systemsof the present invention, differing from one another only in the type ofresistance used in the cathode lead.

Referring to the drawing, wherein like parts are represented by likereference characters, there is shown in each of Figs. 1 and 2 anoscillation generation system comprising an evacuated electron dischargedevice having a control grid G, a cathode K, a screen grid SG, and aplate P. Although a screen grid tube has been shown in the drawing, itshould be understood that this is merely illustrative of any type ofvacuum tube having a plurality of electrodes, the invention not beinglimited to a tetrode. In circuit with the cathode K between two pointsthereof, there is a pure resistive impedance R or R. In circuit with thegrid G and plate P, there are, respectively, inductance coils Lg and Lt,both of which are coupled to the coil L of a parallel tuned oscillatorycircuit 0. Coils Lg and 111) may be made of fine resistance wire, orhave resistors connected in series with them in known fashion to preventparasitic oscillation. It should be noted that connections extend fromthe grid circuit, plate circuit, screen grid circuit, and cathodecircuit to a point of common radio frequency potential, such as ground.Fig. 2 differs from Fig. 1 only in the type of resistive impedance usedin the cathode circuit, the resistor R being Application. January 71939,seriarNa-Mar so 2 Claims. (01. 250 -36) shown as an electricallight bulb whose alternating current resistance increases with increasein temperature.

An exposition of the theory and the operation of the invention follows:The pure resistive im- Where gm=the vtran'sconductance of the tubeand e=the vo-ltage'induced' in the grid circuit.

The conditionior oscillation of this :circuit may be derived as follows:e ='a'ttM1i ,1where 2' is the current in coil' La. i

1 The voltage "induced in the tank :circuit O=jwM2i while the voltage.drop in the tank circuit O=ir, where M1 is the mutual inductancebetween the grid coil Lg and the coil Lo of the oscillatory circuit O,and M2 is the mutual inductance between the plate coil Lip and the coilLo of the oscillatory circuit 0.

For sustained oscillation, these two voltages must add to zero.Replacing i by its expression in terms of gm, R, w, M1 and i, thiscondition becomes 7 w M M 1 T Im If the left side of this equation islarger, the amplitude of oscillation will increase with time.

It will thus be seen that if R is large compared to 91. (or in otherwords, if Rgm is large compared to unity) the condition of oscillationis dependent only to a slight degree upon the value of 9111. The circuitis thus stabilized against the efieot of variation of electrodevoltages, change of tubes, or any other factors which affect the valueof mm.

As with any ordinary oscillator circuit however, when the condition forstarting of oscillations is met, these oscillations will build up inamplitude until grid currentflows with a resulting increase in theeffective value of the circuit resistance 1", or else the tube operatesover such a wide range of its characteristic that the effective gm ofthe tube decreases. For either or both of these reasons, the amplitudecomes to a limiting value. In order, however, to limit the amplitude toa value less than that which introduces the additional losses or thenon-linear action mentioned above, the degenerative resistance R may beof the type whose alternating current resistance increases with increasein temperature, as indicated by the electric light bulb R of Fig. 2, sothat as the amplitude of oscillations increases, its alternating currentresistance value increases so that the amplitude of oscillations ismaintained without further increase at a small value which does notintroduce losses in the circuit or distortion in the tube. Theintroduction of such a resistance in other circuit arrangements forvastly different purposes is known and need not be further described.

While an electric light bulb has been mentioned and illustrated in Fig.2, any other type of resistor may be used whose resistance increaseswith increase in oscillation amplitude.

While I have shown and described two specific forms of the invention, itwill be understood that many modifications thereof will be readilyapparent to one skilled in the art without losing the benefits ofsimplicity provided by the present invention. The essential conditionsto be met are that plate circuit should be coupled to the oscillatorycircuit and the oscillatory circuit in turn so coupled to the gridcircuit as to produce a relatively large regenerative grid voltage whichis in phase with the plate current at the resonant frequency, but out ofphase therewith except at resonance, while at the same time the platecurrent produces a slightly smaller degenerative grid voltage which isindependent of frequency.

What is claimed is:

1. In combination, in an oscillation generation system, an evacuatedelectron discharge device having control grid, cathode and plateelectrodes, individual connections each including an inductance coilfrom said control grid and plate electrodes to a reference point, aparallel tuned oscillatory circuit having an inductance coll coupled tosaid coils in said grid and plate connections, and .a resistor havingnegligible shunt capacity connected between said cathode and saidreference point, said resistor having a value as large as possible butwhich will not stop oscillations and being of such type that itsresistance increases with increase in current flow therethrough.

2. In combination, in an oscillation generation system, an evacuatedelectron discharge device having control grid, cathode and plateelectrodes, individual connections each including an inductance coilfrom said control grid and plate electrodes to a reference point, aparallel tuned oscillatory circuit having an inductance coil coupled tosaid coils in said grid and plate connections, and a resistor havingnegligible shunt capacity connected between said cathode and saidreference point, the resistor being such that its value increases withcurrent flow therethrough.

WALTER VAN B. ROBERTS.

